The invention relates to a mask-handling apparatus used in lithographic projection apparatus for imaging of a mask pattern in a mask onto a substrate.
More particularly it relates to a mask-handling apparatus having a load-port module constructed to receive masks, the mask-handling apparatus being constructed and arranged to exchange a mask between the load-port module and the mask holder.
A lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the mask (reticle) may contain a circuit pattern corresponding to an individual layer of the IC, and this pattern can then be imaged onto a target area (die) on a substrate (silicon wafer) which has been coated with a layer of photosensitive material (resist). In general, a single wafer will contain a whole network of adjacent dies which are successively irradiated through the reticle, one at a time. In one type of lithographic projection apparatus, each die is irradiated by exposing the entire reticle pattern onto the die at once; such an apparatus is commonly referred to as a waferstepper. In an alternative apparatusxe2x80x94which is commonly referred to as a step-and-scan apparatusxe2x80x94each die is irradiated by progressively scanning the reticle pattern under the projection beam in a given reference direction (the xe2x80x9cscanningxe2x80x9d direction) while synchronously scanning the wafer table parallel or anti-parallel to this direction; since, in general, the projection system will have a magnification factor M (generally less than 1), the speed v at which the wafer table is scanned will be a factor M times that at which the reticle table is scanned. More information with regard to lithographic devices as here described can be gleaned from International Patent Application WO 97/33205.
Lithographic apparatus may employ various types of projection radiation, such as ultraviolet (UV) radiation, extreme UV (EUV) radiation, X-rays, ion beams or electron beams, for example. Depending on the type of radiation used and the particular design requirements of the apparatus, the projection system may be refractive, reflective or catadioptric, for example, and may comprise vitreous components, grazing-incidence mirrors, selective multi-layer coatings, magnetic and/or electrostatic field lenses, etc; for simplicity, such components may be loosely referred to in this text, either singly or collectively, as a xe2x80x9clensxe2x80x9d.
Up to very recently, apparatus of this type contained a single mask table and a single substrate table. However, machines are now becoming available in which there are at least two independently movable substrate tables; see, for example, the multi-stage apparatus described in International Patent Applications WO 98/28665 and WO 98/40791. The basic operating principle behind such multi-stage apparatus is that, while a first substrate table is underneath the projection system so as to allow exposure of a first substrate located on that table, a second substrate table can run to a loading position, discharge an exposed substrate, pick up a new substrate, perform some initial alignment measurements on the new substrate, and then stand by to transfer this new substrate to the exposure position underneath the projection system as soon as exposure of the first substrate is completed, whence the cycle repeats itself; in this manner, it is possible to achieve a substantially increased machine throughput, which in turn improves the cost of ownership of the machine. The apparatus may also have more than one mask table and may comprise components which are operated in vacuum, and are correspondingly vacuum-compatible.
A mask present on the mask table will be exchanged for another one when another mask pattern is required for imaging. The latter mask has to be discharged from the mask table and another mask has to be taken from some location and loaded on the mask table. The exchange process may take some time, which will result in a decreased throughput of the lithographic projection apparatus.
An object of the present invention is to provide a mask handler in a lithographic projection apparatus that enables a very short reticle exchange process to yield an improved throughput of substrates and therefore an improved cost of ownership of the apparatus.
According to the present invention there is provided a lithographic projection apparatus for imaging of a mask pattern in a mask onto a substrate, said apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of radiation;
a mask table provided with a mask holder constructed to hold a mask;
a substrate table provided with a substrate holder constructed to hold a substrate;
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; and
a mask-handling apparatus comprising a load-port module constructed to receive masks, the mask-handling apparatus being constructed and arranged to exchange a mask between the load-port module and the mask holder, characterized in that
the mask-handling apparatus further comprises a first robot and a second robot, the first robot being constructed and arranged to exchange a mask between the load-port module and the second robot, and the second robot being constructed and arranged to exchange a mask between the first robot and the mask holder.
The first and second robots allow for a concurrent exchange of a mask at the load-port module and of a mask at the mask table, and the configuration may be designed such that the first robot presents a new mask to the second robot at the moment a mask should be interchanged on the mask table for another one. Both robots may be designed for their specific tasks in a mask-handling sequence, the second robot being constructed such that the actual transfer to the mask holder of the mask table takes place very fast and efficiently.
An embodiment of such a second robot is provided with two mask holding arrangements, which allows placement of a new mask in one of the mask holding arrangements before or during unloading of a mask from the mask table in another one of the mask holding arrangements. Removal of the unloaded mask and supply of the new mask may then take place in one quick action. Preferably, the second robot is rotatable, for instance like a carousel, for a very quick and efficient transfer of the new mask to the mask table by a simple rotation.
In a further embodiment each mask holding arrangement of the second robot comprises an elevator constructed to exchange a mask between the second robot and the mask holder, and the elevators may be provided with vacuum-operated end-effectors constructed to hold a mask at its top side.
The load-port module, the robots and the mask holder may be understood as mask stations that are constructed to receive a mask. In yet a further embodiment, the mask-handling apparatus comprises one or more further mask stations constructed to receive a mask, the first robot being constructed and arranged to exchange a mask between one of the load-port module, the second robot and the further mask station or stations and another one of the load-port module, the second robot and the further mask station or stations. The further mask station or stations may comprise a mask library constructed and arranged to store one or more masks, and/or a mask inspection station constructed and arranged to check a mask for contamination. Such further mask stations improve the functionality of the mask handler, and the two-robot configuration allows the first robot to be constructed such as to be able to exchange a mask between the various stations while the actual exchange of masks at the mask table may still take place very fast.
A conveniently constructed first robot has an arm-like configuration provided with three rotary joints such as to allow movement in a plane. Such a configuration allows mask to be exchanged readily between various mask stations positioned such that they may be accessed in the plane of movement of the first robot. It allows translation of the mask in at least such a plane in which the mask stations may be provided, and it also allows the mask to be rotated about an axis that is perpendicular to said plane for efficiently orienting and translating a mask towards a mask station. The first robot may further comprise a linear actuator such as to allow for a translation in a direction perpendicular to said plane to be able to access mask stations that are offset at various height levels or various height levels within one mask station, for instance the mask library.
To allow the first and second robots to be aligned with respect to each other during exchange, and to allow the second robot and the mask holder to be aligned with respect to each other, the mask-handling apparatus preferably further comprises at least one pre-alignment unit constructed and arranged to detect a position of a mask held by one of the first robot, the second robot and the mask holder, the or each pre-alignment unit being associated with a position of the second robot allowing for exchange of a mask with one of the first robot and the mask holder.
According to yet a further aspect of the invention there is provided a method of manufacturing a device using a lithographic projection apparatus comprising:
an illumination system constructed and arranged to supply a projection beam of radiation;
a mask table provided with a mask holder constructed to hold a mask;
a substrate table provided with a substrate holder constructed to hold a substrate;
a projection system constructed and arranged to image an irradiated portion of the mask onto a target portion of the substrate; and
a mask-handling apparatus comprising a load-port module constructed to receive masks, the mask-handling apparatus being constructed and arranged to exchange a mask between the load-port module and the mask holder, said method comprising the steps of:
providing a mask bearing a pattern to the mask holder;
providing a substrate which is at least partially covered by a layer of radiation-sensitive material to the substrate table; and
using the projection beam of irradiation to project an image of at least a portion of the mask pattern onto a target portion on the substrate, characterized in that
said step of providing a mask bearing a pattern to the mask holder comprises the sub-steps of:
providing the mask to the load-port module;
using a first robot provided in the mask-handling apparatus to exchange the mask between the load-port module and a second robot provided in the mask-handling apparatus; and
using the second robot to exchange the mask between the first robot and the mask holder.
In a manufacturing process using a lithographic projection, a pattern in a mask is imaged onto a substrate which is at least partially covered by a layer of energy-sensitive material (resist). Prior to this imaging step, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book xe2x80x9cMicrochip Fabrication: A Practical Guide to Semiconductor Processingxe2x80x9d, Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4.
Although specific reference has been made hereabove to the use of the apparatus according to the invention in the manufacture of ICs, it should be explicitly understood that such an apparatus has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms xe2x80x9creticlexe2x80x9d, xe2x80x9cwaferxe2x80x9d or xe2x80x9cdiexe2x80x9d in this text should be considered as being replaced by the more general terms xe2x80x9cmaskxe2x80x9d, xe2x80x9csubstratexe2x80x9d and xe2x80x9ctarget areaxe2x80x9d, respectively.